last night, Irish a raoir,
a réir,
Old Irish aréir, *pre-ri,
root as in
riamh (Asc.,
St.). The Sanskrit râtri, night, has been
compared, but the phonetics do not suit, and also Latin retro.
Cf. also
earar,
uiridh.

surety, vadimonium, Irish
rath (
O'Br.,
O'Cl.),
Old Irish
ráth; cf.
Old Breton rad, stipulationes, which Stokes equates with
Irish
rath, and says that it is from Latin ra@utum (ratum facere =
"ratify"), a derivation to which Loth objects. Hibernian
Latin has rata for surety. The Latin and Gaelic are ultimately
from the same root in any case (see ràdh).

frost, Irish reó, reodhadh,
Early Irish reo, reod,
Old Irish reúd,
Welsh rhew, Cornish reu, gelu, Breton reo, rev. Stokes gives the stem
as *regu-, even suggesting that the Gadelic forms are borrowed
from the Cymric;
Old Irish réud he refers to *presatu-. Indo-European
preus, whence Latin pruina, English freeze, has been suggested,
but the vowels do not immediatley suit (preus would give
rua-, ró- or ro-, in Gaelic); yet *prevo-, a longer form (with or
without s) of preu-s, can account for the Celtic forms.

cut the surface, graze. Although there is Indo-European reiko-,
notch, break (Greek
@Ge@'reíkw, tear, Lit raiky/ti, draw a furrow,
etc., German reihe, row, English row), yet it seems most probable
that riach is a variant of
strìoch, q.v.